Spark-plug.



D. M. DUNNING. 1111 SPARK PLUG.

APPLlcATmN m51) AuG.24, 1910. BENEwED Nov. 15. 1916.

Patented Dec. 26, 1916.

PATENT FFG 9 quam is' AUBURN, 1

IUE@ fl-' "D ST terior of the collar, a short annular skirt 1 0, to prevent the possible formation of a moisture film between the collar and the metallic shell. The projecting, threaded stem of the inner electrode also carries an ordinary tliumb-iiut ll such as common on bindingposts, and constituting means for att a ch ment of the circuit terminal of the ignition system. Both nuts, 'as well as the collar, can be cheaply made, the former in the automatic lathe and the latter in molding machines.

The electrodes proper' may either be formed on or attached to the extremities of the shell and inner core as desired, but l pre.

fer an arrangement; wherein these parts are separately made, out of special wire alloy,- and subsequently secured in position on the shell and core as shown in the drawings. The central electrode 12 vill thus project from the inclfsed head of the core 8, through the center oi the inner compartment or recess 6, while the other electrode 13 will bend ovei' from the shell to within a sparking distance Ifrom it. As thus arranged it will be observed that the two electrodes and their metallic supports will be separated by both of the annular cavities 5 and 6, constituting a. most effective barrier against short-circuiting. It is well known that a cavity, such as either of these, located between the opposite terminals of the plug, will operate to prevent the deposit of cai'bon which might foi-in a conducting bridge and cause a shortcircuit. It will be observed that the larger end of the central core 8 projects within the sleeve 4 beyond the outer end or bottom of the cavity 5, thereby internally supporting the sleeve within said recess.

The security with which the parts above described are held in place by the clamp nut, while sufficient under all normal conditions, is not entirely reliable in that the said nut may become accidentally loosened either by revolving with the thumb-nut ll or by the effect of constant vibration of the engine, or by the stripping of its threads during the course of manufacture., in any of which cases the inner core is likelyI to slip back and quickly render the plug useless, if italoes not, indeed, fall into the cylinder and break the engine.. To guard against this contingency l provide on each of the two metallic members a spur or projection which will dig into andbecome firmly seated in the mica sleeve when the parts are wedged home. rThe spur on the inner core meinber is .formed by slightly battering or up` setting its large end to form a shut or iin thereon, as indicated in an exaggerated nianner at 14 in Fig. al.. The spur on the shell is located at its upper margin, as indicated at i5 in the same figure, and may be similarly made. ln either case the fin or projection may extend continuously around the Maur/,onu

core or the margin of the shell, or it may only be present at one or more points, provided tlie three tapered members of the `device are thereby safely held together inaltogether, as`

tion of an externally threaded electrodebearing shell having a tapered bore extend-4V ing to the outer end of the shell, a correspondingly tapered sleeve of rolled sheet mica in said bore, a similarly tapered electrode-bearing core within said sleeve, a solid collar of non-vitreous compressiblc insulating material surrounding and protecting the mica sleeve which projects from the outer end of the shell, a clamp nut threaded to the core for drawing the tapered parts together and compressing said collar against the shell, said shellv and core being provided with projecting spurs which are forced into the outside and inside of the sleeve when the parts are drawn together by said nut, and a terminal attachment nut on the core.

2. A spark-plug comprising a threaded shell having a recess in its threaded end and a tapered bore of less diameter than the recess extending therefroin to and through the outer end of the shell, a correspondingly tapered electrode-bearing core in said bore, a similarly tapered rolled sheet mica sleeve between the core and bore extended into and terminating in the said yond the inner end of the said tapered core, thereby forming two concentric, open compartments and electrodes respectively secured to said shell and core and separated by the two open insulating compartments and the end of the mica sleeve, in combination with a solid collar of non-vitreous compressible insulating material surrounding and protecting the end of the mica sleeve and bearing against the outer end of the shell, the sleeve embracing` hole therethrough being slightly longer than the projecting end of the sleeve, a clamp nut threaded on said core and clamping the parts together, and a terminal attachment-nut on said core.

3. A spark-plug comprising an electrodebearing threaded shell` having a recess in its threaded end and a tapered bore of less diameter than the recess extending therefrom to` and through the outer end of the shell` a correspondingly tapered electrode-bearing core in said bore, and a similarly tapered rolled sheet mica sleeve between the core and bore extended into and terminating in the saidrecess at a point beyond the inner end of the said tapered core, thereby forming two concentric,

open compartments, the

recess at a point be larger end of said core projecting beyond In testimony whereof, I have signed this the bottom of the recess in the shell, in com specification n the presence of two Wit* 10 bnzttion with a solid collar of non-vitreous nesses.

compressible insulating-material su'round- I 5 ing and protecting the end` of the mica DAVID M' DUNNING JR sleeve, and a nut threaded on said core be- Vitnesses: yond said collar and clamping the parts to- HUBERT B. ROMIG,

gether. l, SEYMOUR H. KNOX. 

